The present invention relates to surgical instruments and in particular to a jig assembly used in orthopaedic surgery.
Knee replacement surgery is complex and requires the bone surfaces to be prepared. In particular femoral and tibial resectioning, in which a saw or other cutting tool is used to prepare bone surfaces to receive surgical implants, is required. In order to carry out these surgical techniques a number of tools and instruments can be used to assist the surgeon in carrying out the procedure appropriately.
A cutting block is usually used in order to guide the saw during the resection procedure. The cutting block is mounted and secured at the appropriate position on the bone surface. The correct positioning of the cutting block may be assisted by means of a jig and/or other alignment and support tools.
In the case of a tibial resectioning procedure, a tibial jig can be used in order to align a cutting block with respect to the longitudinal axis of the tibia. The tibial jig comprises a rod which can be in two parts to accommodate different tibia lengths. An appropriate cutting block is mounted on the rod, aligned at the proximal end of the tibia, and then secured in place by means of pins.
The cutting block defines an upper surface for guiding the cutting tool and may have a slot which can also be used as a cutting tool guiding surface. The slot can also be used as a means to attach other instruments such as a condylar stylus, or an alignment and adjustment tool. The jig may also include a mechanism for adjusting the flexion/extension slope of the cutting tool guiding surface.
One such tibial jig is the one designed for use with the Attune® knee prosthetic system from De Puy Synthes.
Some surgeons prefer to have the additional assistance provided by a spiked jig. The spiked jig that includes a rod which is aligned parallel to the tibia in the same way as the jig referred to above, but also includes a head which extends perpendicularly to the rod at a position that extends beyond the proximal end of the tibia at the knee joint. The head is mounted onto the rod by means of a mounting rod. The head includes a number of downwardly extending spikes which can be inserted into the tibia at the tibial eminence. One spike is longer than the other. During surgery, the surgeon is able to hammer only the longer spike in, make any adjustments to the rotation of the instruments that may be required, before hammering in the second, shorter spike. The cutting block is supported by the rod and mounted at an intermediate location on the tibia. The cutting block is therefore mounted partially along the rod rather than at the end as with the jig described above.
While the spiked jig provides additional stability for the surgeon, there are a number of disadvantages:                The positioning of the mounting rod obscures access to the cutting block, thus preventing the use of alignment rods which are secured to the cutting block.        It is not possible to provide a variable guiding surface slope mechanism because the presence of a mounting rod in front of the cutting block prevents this. It is therefore necessary to use additional blocks with guiding surfaces at predetermined and varying sloping angles which can be mounted onto the jig. This creates a large inventory of instrumentation        If any further adjustments are required during the surgical procedure then this means that the whole spiked uprod needs to be removed to allow a cutting block change.        The profile of the head is such that a special condylar stylus is required in order to measure both tibial condyles.        